The present invention generally relates to the manufacture of integrated electronics. More specifically, the invention relates to methods for laterally limiting single crystal regions in substrates.
Laterally limited, single-crystal regions that are produced by selective epitaxy at the surface of a substrate within limiting structures are increasingly employed in semiconductor technology. For example, European patent EP 0 418 422 A1 discloses a bipolar transistor whose collector is manufactured by selective epitaxy within a region on the surface of a substrate limited by oxide structures. However, high demands must be made of the crystal quality upon employment of such a single-crystal region produced by selective epitaxy as active part of a transistor.
In selective epitaxy on a substrate of, for example, silicon within a limiting structure of, for example, silicon oxide, the deposition conditions for the silicon are set such that only the silicon grows on silicon surfaces. Since the silicon grows only according to the orientation of the surface of the substrate, a single-crystal region thereby arises within the limiting structure. It has been observed, however, that the single-crystal region has crystal defects in the parts or portions thereof neighboring the limiting structure.
When using a single-crystal region produced by selective epitaxy as an active part of a transistor, for example as base, it is also desirable to laterally connect the single-crystal region via a correspondingly doped polycrystalline silicon layer. It would therefore be desirable to grow the single-crystal region within a limiting structure on polysilicon. The problem arises, however, that silicon grows not only on the single-crystal surface of the substrate but also on the exposed surfaces of the polycrystalline silicon layer. Since the surface of the polycrystalline silicon layer does not have a uniform crystal orientation, grain limits therefore arise in that part of the single-crystal region growing on the polysilicon to such an extent that these parts can no longer be referred to as single-crystal. Such a selectively grown silicon region can no longer satisfy the demands made of the crystal quality for an active part of a transistor.